Microscopic polyangiitis

Microscopic polyangiitis is a rare autoimmune disease in which the body's immune system attacks the walls of small blood vessels, causing a type of inflammation called necrotizing vasculitis that damages tissue without forming the clusters of inflammatory cells known as granulomas that mark related conditions. The kidneys are affected in up to eighty percent of cases, often leading to a rapidly progressing form of kidney inflammation, while the lungs are involved in twenty to fifty percent of cases and can bleed internally in severe episodes. The disease is also known to affect the skin, nerves, and digestive tract. Its development is linked to antibodies called perinuclear antineutrophil cytoplasmic antibodies, or p-ANCA, which target an enzyme called myeloperoxidase in white blood cells and drive the vessel damage. Researchers believe the condition requires both a genetic predisposition and an environmental trigger, such as an infection, an underlying cancer, or certain medications, to activate the abnormal immune response. The disease is also known by the older name Wohlwill's disease. Treatment usually combines corticosteroids with immune-suppressing medications to bring the vasculitis under control and protect organ function.